1. Field of the Invention
This invention relates to the formation of monolithic semiconductor circuits having an IMPATT device as a portion thereof, the IMPATT device being structured to provide maximum heat sinking through the substrate.
2. Description of the Prior Art
Monolithic semiconductor circuits wherein complete circuits are provided on a single semiconductor substrate have been well known for many years. Such prior art semiconductor substrates have had the advantage of close proximity to each other of the circuit elements therein, this feature being extremely important as the frequencies utilized increase. These prior art monolithic circuits have required that all of the components be formed in a substrate containing a single semiconductor material and have also required that the processing steps for all of the components therein be compatible with each other within the bounds of economics. For this reason, when it has become necessary to provide circuits utilizing substrates of differing semiconductor materials or of the same semiconductor material but wherein the processing steps were incompatible, it has been necessary to use a plurality of semiconductor chips to provide the desired circuit configuration. A typical example of this problem exists in the fabrication of a circuit utilizing an IMPATT structure and associated circuitry containing FETs, varactors, etc., wherein operation is in the microwave region. In such cases, it is necessary, due to the totally incompatible processing techniques in formation of IMPATTs relative to other standard circuitry, that the IMPATT be formed on a separate semiconductor chip. This has presented a problem in the prior art in that it is desirable that the components be as close together as possible in the microwave operating region to prevent a limit in device performance due to the transitions that exist.
In addition to the above, it is well known that IMPATT devices dissipate a great deal of heat and require efficient heat sinking for proper operation. This has created a problem in the past because the gallium arsenide substrate material is not a very good heat sink and is capable of conducting only approximately one-tenth the amount of heat that a similar amount of gold or silver is capable of conducting. One prior art approach, wherein a monolithic circuit is provided utilizing an IMPATT and other circuit components, is set forth in my copending application Ser. No. 630,489, filed July 13, 1985, wherein a metal heat sink is formed to extend through the monolithic circuit, thereon. This approach requires the additional steps of forming the metal heat sink. It is therefore desirable to create monolithic circuits of the type described herein and in said copending application wherein the processing steps required can be minimized.